Power plants come in many different shapes and sizes. Large power plants can be used to provide electricity to a geographic area, whereas relatively small power plants can be used to power local areas or submarines or space craft, for example. In addition to providing electricity, power plants can be used for a myriad of additional or different purposes, from desalinating sea water to creating nuclear isotopes for medical purposes. Similarly, the types of power plants that are available cover a wide spectrum of technologies including gas powered, coal fired, and various types of nuclear power, to name a few.
One common feature between many of these power plants is the production of energy in the form of heat. Typically, the heat that is produced is ultimately used to convert water into steam. When the production of electricity is the desired goal, the steam is typically used to run a turbine. Regardless of the source of the heat, a heat transfer system is used to transfer the heat generated by the power plant to the water that is then converted to steam. In most nuclear power plants, a heat exchanger comprising a number of straight-through, once-through, or U-shaped tubes is used to exchange the heat between a primary coolant circulating through the reactor core and a secondary coolant that is converted to steam.
The tubes are relatively simple to manufacture and install using mechanical methods of connecting the tubes to a tube sheet. The tubes are typically friction or pressure-fit to the tube sheet by roll-expanding a portion of the tubes within the tube sheet using a mechanical, pneumatic, or hydraulic device to provide a leak tight joint. However, by expanding the tubes, this causes a plastic deformation that leads to a weakened state of the tube wall and serves as a potential point of failure. Furthermore, the tube design requires a sufficient amount of surface area to provide the thermal efficiencies necessary to transfer the heat to the secondary coolant system. Accordingly, a corresponding amount of space must be provided to accommodate the resulting length of the tubes.
The present invention addresses these and other problems.